Process for making a stencil screen coating and composition therefor



3 176 7 2 rsoesss son name A srnNcrL scnEEN COAT- llNG AND CGMPOHTIONTHEREFOR Clarence T. Cunningham, Alton, E11,, assignor to OwensliilinoisGlass Company, a corporation of ()hio No Drawing. Filed Feb. 10, 1961,Ser. No. 88,297 11 Claims. (Cl. 9635) dye are added to the solution. Thepurpose of the dye is to make the composition more' visible so that theultimate user of the screen can readily perceive which portion of thescreen is coated therewith. The viscous gelatin solution is then coatedonto a fine mesh screen, either by applyingthe viscous mass vw'th asqueegee, or by immersing the screen while flat in a shallow pancontaining some of the composition so that the composition will justpenetrate the interstices of the screen so as to smround them andprovide a physical bond to the Screen.

The light-sensitizing agent enables a photographic procest: to be usedin converting the coated screen into a stencil outlining the desiredpattern. A film in the nature of an opaque positive of the desireddecoration or printing is placed over the fine mesh screen coated withthe light-sensitized composition, and this assembly is exposed to alight source, such as an arc lamp. The arrangement is such that thelight issuing therefrom will pass through the negative and contact thecoated screen at those areas outlined by the transparent portion of thenegative. The light contacted composition is converted to a state of3376,79? PatentedFeb. 23, 1965 In an effort to enhance the life of thesescreens, the art has resorted to several modifications. In oneembodiment, the screen which has been coated with the gelatincomposition in the desired pattern, and dried (as described above) isdipped into a glycerin bath. The glycerin adheresto the coated stencilscreen, and the screen is then again dried. The glycerinovercoat isfound to impart a slight increase in strength to'. the coating and,consequently, slightly longer life to the stencil in the automaticequipment. Another embodiment which has been utilized involves theinclusion of glycerin in the melted gelatin solution. Glycerin, beingwater soluble, readily goes into solution with the water containing themelted gelatin. It has been found that this also slightly upgrades thecoating concentration, thereby increasing the life of the screen formedtherefrom. Unfortunately, neither of the above embodiments is soadvantageous that it really justifies the expense of the modification.Thus, the'coating of the stencil screen with glycerin involves an extrastep in the manufacture of the screens and consequently increasesthecost. Further, the cost of the glycerin itself addsv to the expenseof the ultimate screen.

Accordingly, it is an object of the present invention to provide animproved. stencil screen masking composition which permits theproduction of a stencil screen possessed of longer life than those knownheretofore.

It is another object of this invention to provide such a stencil screencoating composition which is relatively inexpensive, can be produced bya relatively simple process, and yet yields a stencil screen of improvedquality.

It is yet another object of this invention to provide a stencil screencomposition which, by reason of its greater water insolubility, whereasthe portion of the composition 1 which is not contacted bylight remainswater soluble.

The coated screen is then given a mild wash with water to remove thewater soluble portion and thereby yield the final stencil which bears acoating outlining the desired decoration or printing. The portion of thescreen bearing the water-insoluble coating composition has itsinterstices filled with this composition so that the decoratingmaterial, such as'a printing ink, paint, vitreous enamel, glaze, orcolorYwill not pass therethroughf Stencil screens so producedare-conveniently used to apply color or printing to a substrate such asglassware, e.g., bottles, tumblers, and the like. The stencil held in aframe is brought into contacting relationship with a tumbler or bottleheld in a chuck. Decorating medium or color on the screen is then forcedthrough the unfilled interstices of the stencil screen by a squeegeeonto the underlying surface in the desired pattern. After either thestencil or the bottle is retracted so as to be separated from contactwith the other, the bottle, or tumbler passes into an oven for making,in the case of heat-hardenable 7 invention.

strength and consequent longer life, materially reduces the down timefor the automatic equipment used in applying decorations to a substrate.

It is still another object of this invention to provide a compositionwhich is tougher and less apt to crack under rigorous service conditionsencountered with automatic color decorating and printing machines.

The above and many other objects, features, and advantages of thepresent invention will become apparent to those skilled in the art fromthe following detailed description and the examples set forthbelow, inwhich reference will he had to several preferred embodiments.

Basically, the present invention is predicated upon the discovery thatan improved gelatinous stencil screen masking composition may beproduced by including in the aqueous solution of gelatin an ester of analiphatic car: boxylic acid including, for example,the alkyl esters ofmalonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic,oleic, linoleic, 'linolenic, and eleostearic acids, wherein the alkylsare straight chain or branched and contain from 2 to 10 carbon atoms.Each carboxyl group of the acid has an alkyl radical attached thereto.

The following examples are merely illustrative of the Example 1 Animproved stencil screen composition of the present invention wasprepared according to the following formulation:

i 1000 cc. water 230 grams sheet gelatin 250 cc. (217 gramsl butyloleate using density of 0.868 gm./ml.)

12 grams of a blue paste dye (Monastral Fast Blue 20 grams sodiumbichromate The above ingredients were combined in the following manner:cc. of'water at a temperature of 180 F. was poured into a glue pot. Thedye and gelatin were added, and the mixture heated to about F. The

(weight calculated heat was maintained until the gelatin had gone intosolution (about 30 minutes). Next, the butyl oleate was added to thesolution and the mixture stirred. In a separate container, the sodiumbichromate was dissolved in 400 cc. of hot water, and this solution waspoured into the gelatin solution and mixed until blended. This tookabout three minutes. Next, hot water was run through a colloid mill tobring the mill up to the same temperature as the previously preparedmixture, e.g., about 175 F. When the mill was thus warmed, thegelatinous mixture was run through the mill five times in order to moreor less homogenize the ingredients. The completely mixed composition wasthen strained through a 165 mesh stainless steel screen into a shallowpan maintained at about 140 F. It was allowed to set for about fiveminutes to allow air bubbles to rise to the surface of the liquid. Theexposed surface of the liquid was then scraped to remove the bubbles sothat the screen could be floated. To float a screen, it is held in ahorizontal position and immersed in the composition so that the topsurface is just covered by the liquid composition. When it is liftedslowly therefrom, the bottom side of the screen will be found to be moreheavily coated than the top side. The composition just penetrates theinterstices of the screen as described hereinbefore to insure its beingretained thereby. The coated screen was then dried in a darkroom, afterwhich an opaque positive film of the desired design, in which theultimately desired printing or lettering corresponds to the opaque partof the film and the remaining areas thereof are translucent so as topermit transmission of light therethrough, was placed over the screen,and the assembly exposed for about one minute to light issuing from anarc lamp located on the film side of the assembly. The portion of thecomposition contacted by light is converted thereby to a cured statewhich is insoluble in water. The screen was given a mild wash with warmwater, whereupon the portion of the coated screen which had not beenexposed to light washed away, leaving the stencil screen bearing a waterinsoluble coating which outlined the desired decoration, printing, orthe like. This stencil screen was found to be extremely tough ascompared to the conventional gelatin screens or to the gelatin screenswhich had been modified by overcoating with glycerin or combiningglycerin with the melted gelatin in the formulation thereof. The stencilscreen was not subject to cracking, and was capable of undergoing asubstantially greater number of cycles in automatic decorating equipmentwithout material degradation.

Example II An improved stencil screen coating composition of theinvention was prepared according to the same formulation and in the samemanner as described in connection with Example I, except that 250 cc. ofdi-2 ethylhexyl adipate (242 grams calculated using density of 0.927gm./ml.) was substituted for the 250 cc. of butyl oleate. It was foundthat the composition yielded a stencil screen which was possessed of thesame desirable qualities as the stencil produced according to Example I,e.g., longer life, tougher, non-cracking, and, at the same time,relatively inexpensive.

Example III Following the aforesaid procedure, 25 gm. of solid granulargelatin, technical grade, was dissolved in 100 gm. of water. To this wasadded 1 gm. of solid Monastral Blue dye and 4 gm. of potassiumdichromate light sensitizer. This solution was combined with 25 gm. ofdiethyl adipate and blended for 5 min. The resulting solution wasapplied to a stencil screen and exposed by an arc lamp. The imageproduced was clear and sharp, and the stencil screen produced had thesame desirable qualities as in Examples I and II.

Example IV Again following the aforesaid procedure, 25 gms. of

solid granular gelatin, technical grade, was dissolved in 100 gm. ofwater. To this was added 1 gm. of solid Monastral Blue dye and 4 gm. ofpotassium dichromate light sensitizer. This solution was combined with25 gm. of di-Z-ethylhexyl adipate and blended for 5 min. The resultingsolution was applied to a stencil screen and exposed by an arc lamp. Theimage produced was clear and sharp, and the stencil screen produced hadthe same desirable qualities as in the aforesaid examples.

In order to achieve the optimum combination of the desirablecharacteristics mentioned, it is preferred that the aliphatic carboxylicacid ester be present in the composition in about equal weightproportion with respect to the gelatin.

However, tests have shown that the gelatin may be present in amounts offrom 33 to parts by weight and the carboxylic acid ester may be presentin amounts of from 67 to 20 parts by weight, based upon the combinedweight of the gelatin and the ester.

Exactly why the modification of gelatin by the inclusion of an alkylester of a carboxylic acid, such as butyl oleate, di-Z-ethylhexyladipate, di-ethyl adipate and the like advantageously improves theproperties in the manner described is not known. However, and althoughit is not intended to be bound by any theory expressed herein, it ispossible that these materials, although being water insoluble (whereasglycerin is water soluble), contribute an internal physicalplasticization and thus lend to the final composition a resiliency whichis reflected in the improved service performance of the stencil screens.

Other light-sensitizing agents than sodium bichromate may, of course, beused in forming the masking compositions of this invention. Thus, any ofthe conventional light-sensitizing agents (essentially oxidizingmaterials) may be used, although the dichromates of potassium, sodium,and/or ammonium are preferred.

The composition of this invention may be applied to metallic wirescreens or to silk nylon screens with equal facility. Where applied towire, the composition may be removed by burning it off with flame, thuspermitting the wire screen to be salvaged and reused, if desired. Fornylon or silk screens, a solution of bleach such as hypochlorite isconveniently used to remove the composition.

While there have been disclosed certain preferred embodiments of theinvention, it is not thereby desired or intended to be limited solelythereto, for the precise proportions of the materials utilized may bevaried and equivalent chemical materials may be employed, if desired,without departing from the spirit and scope of the invention as definedin the appended claims.

Having fully described the invention, what is claimed l. A stencilscreen comprising a screen base and a coating on said screen base, saidcoating filling the voids of the said stencil screen and whereinsubsequently portions of said coating are removed according tophotographic methods in order to form a preselected pattern on saidscreen, said coating comprising an aqueous mixture of (a) gelatin, (1))a light-sensitizing agent to permit photographic method production ofthe design pattern. and (c) a member selected from the group consistingof the alkyl esters of malonic, succinic, glutaric, adipic, pirnelic,suberic, azelaic, sebacic, oleic, linoleic, linolenic and eleostearicacids, said alkyl containing from 2 to 10 carbon atoms, and the amountof (a) being from 33 to 80 parts by weight based on the combined weightof (a) and (c).

2. A stencil screen as defined in claim 1 wherein the alkyl ester isdi-Z-ethylhexyl adipate.

3. A stencil screen as defined in claim 1 wherein the alkyl ester isbutyl oleate.

4. A stencil screen as defined in claim 1 wherein the alkyl ester isdiethyl adipate.

5. A stencil screen comprising a screen base and a coating on said base,said coating filling the voids of the said stencil screen and whereinsubsequently portions of the coating are removed according tophotographic methods to form a preselected pattern of voids on saidscreen, said coating composition comprising an aqueous mixture of (a)gelatin, (b) a light-sensitizing agent to permit photographic methodproduction of the desired pattern, and (c) a member selected from thegroup consisting of the alkyl esters of malonic, succinic, glutaric,adipic, pimelic, suberic, azelaic, sebacic, oleic,. linoleic,

' linolenic and eleostearic acids, said alkyl containing from screen andwherein subsequently portions of the coating are removed according tophotographic methods of production to form a preselected pattern ofvoids on said screen, said coating comprising:

G. Water 1000 Gelatin 230 Butyl oleate 217 Dye l2 Dichromatelight-sensitizing agent 20 10. The stencil screen comprising a base anda coating on said base, said coating filling the voids of said stencilscreen and wherein subsequently portions of the coating are removedaccording to photographic methods of production to form a preselectedpattern of voids on said screen, said coating comprising:

G. Water 1000 Gelatin 230 Di-Z-ethylhexyl adipate 242 Dye l2 Dichroniatelight-sensitizing agent 20 1 1. In the method of forming a preselectedpattern of voids on a stencil screen comprising the steps or" fillingthe voids of said stencil screen with a coating of an aqueous mixture ofgelatin and a light sensitizing agent, drying said coating on saidscreen, placing an image containing member having transparent andnon-transparent portions before said screen, exposing said screen to alight passing through said transparent portion of said image containingmember, that portion of the gelatin coating in said voids of said screencontacted by said light being rendered water insoluble, the remainder ofsaid gelatin coating on said screen remaining water soluble, and washingsaid screen to remove said water soluble portion of said gelatincoating, said voids containing said water insoluble coating thusdefining a pattern of the configuration of the transparent portion ofsaid image containing member, the improvement whereby said aqueousmixture of gelatin and a light sensitizing agent contains a memberselected from the group consisting of alkyl esters of malonic, succinic,glutaric, adipic, pimelic, suberic, azelaic, sebacic, oleic, linoleic,linolenic, and eleostearic acids, said alkyl containing from 2 to 10carbon atoms, and the amount of gelatin being from 33 to parts by weightbased on the combined weight of gelatin and alkyl ester.

References Cited by the Examiner UNITED STATES PATENTS 2,322,026 6/43Jelley et al 96-97 2,685,510 8/54 Yackel 96-35 XR 2,937,088 I 5/60 Grayet al 96-94 2,940,854 6/60 Gray 96-94 2,943,936 7/60 Spechler 96-35 XR2,980,534 4/60 Printy et al 9693 XR OTHER REFERENCES Doolittle: TheTechnology of Solvents and Plasticizers, John Wiley and Sons, New York,1954, pp. 951, 952 and 962.

Koslofi: Screen Process Printing, Signs of the Times Pub. Co.,Cincinnati, Ohio, 1950, pp. 91-97.

NORMAN G. TORCHIN, Primary Examiner.

MILTON H. STERMAN, HAROLD H. BURSTEIN, Examiners.

11. IN THE METHOD OF FORMING A PRESELECTED PATTERN OF VOIDS ON A STENCILSCREEN COMPRISING THE STEPS OF FILLING THE VOIDS OF SAID STENCIL SCREENWITH A COATING OF AN AQUEOUS MIXTURE OF GELATIN AND A LIGHT SENSITIZINGAGENT, DRYING SAID COATING ON SAID SCREEN, PLACING AN IMAGE CONTAININGMEMBER HAVING TRANSPARENT AND NON-TRANSPARENT PORTIONS BEFORE SAIDSCREEN, EXPOSING SAID SCREEN TO A LIGHT PASSING THROUGH SAID TRANSPARENTPORTION OF SAID IMAGE CONTAINING MEMBER, THAT PORTION OF THE GELATINCOATING IN SAID VOIDS OF SAID SCREEN CONTACTED BY SAID LIGHT BEINGRENDERED WATER INSOLUBLE, THE REMAINDER OF SAID GELATIN COATING ON SAIDSCREEN REMAINING WATER SOLUBLE, AND WASHING SAID SCREEN TO REMOVE SAIDWATER SOLUBLE PORTION OF SAID GELATING COATING, SAID VOIDS CONTAININGSAID WATER INSOLUBLE COATING THUS DEFINING A PATTERN OF THECONFIGURATION OF THE TRANSPARENT PORTION OF SAID IMAGE CONTAININGMEMBER, THE IMPROVEMENT WHEREBY SAID AQUEOUS MIXTURE OF GELATIN AND ALIGHT SENSITIZING AGENT CONTAINS A MEMBER SELECTED FROM THE GROUPCONSISTING OF ALKYL ESTERS OF MALONIC, SUCCINIC, GLUTARIC, ADIPIC,PIMELIC, SUBERIC, AZELAIC, SEBACIC, OLEIC, LINOLEIC, LINOLENIC, ANDELEOSTEARIC ACIDS, SAID ALKYL CONTAINING FROM 2 TO 10 CARBON ATOMS, ANDTHE AMOUNT OF GELATIN BEING FROM 33 TO 80 PARTS BY WEIGHT BASED ON THECOMBINED WEIGHT OF GELATIN AND ALKYL ESTER.